2026-08-22 13:41:24 -04:00
21 changed files with 1046 additions and 127 deletions
@@ -172,6 +172,8 @@ endpoint at `/mcp`, not these REST routes.
 | GET | `/api/plugin/context` | SessionStart context payload (rules + active-project) |
 | GET | `/api/plugin/retrieve` | Title-first knowledge-injection candidates |
 | GET | `/api/plugin/processes` | Stored Processes for skill-stub sync |
+| GET | `/api/plugin/prior-art` | Write-path hint for the plugin hooks (params: `path`, `code`, `repo`, `shapes`, `exclude_ids`, `exclude_sync_ids`, `exclude_derive`); returns `context`, `note_ids`, `sync_note_ids`, `stamped`, `divergence`, `derive`, `derive_keys` |
+| GET / POST | `/api/projects/<id>/coverage`, `…/coverage/refresh` | Shape-ledger accounting (`pattern_coverage` line, counts, `derive_groups`, `derive_new`, `divergence`, `recheck`) |
 | GET / PUT | `/api/plugin/marketplace-url` | Read / set the plugin marketplace URL |

 ## Dashboard, Export, Trash, Users
@@ -1,7 +1,7 @@
 {
  "name": "scribe",
  "description": "Scribe system-of-record for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, process-skills (writing-plans, systematic-debugging, verification, brainstorming, reusing-code), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
-  "version": "0.1.38",
+  "version": "0.1.39",
  "author": { "name": "Bryan Van Deusen" },
  "mcpServers": {
    "scribe": {
@@ -52,8 +52,18 @@ On install you'll be asked for:
  but never stop it; silent when nothing is recorded, which is most of the time.
  Two framings: a REUSE menu (similar/nearby records), and a SYNC nudge when a
  snippet records the exact file being edited — "updating the record is part of
-  the edit" — each with its own once-per-session dedup.
+  the edit" — each with its own once-per-session dedup. A third, ledger-fed
+  line names a duplicate family (no canon) or a canon recorded elsewhere for
+  the names being written (its own dedup channel, `exclude_derive`).
  Toggle in **Settings → Knowledge auto-inject**.
+- `hooks/hooks.json` → PostToolUse hook on `Bash`
+  (`hooks/scribe_after_write.sh`): code written through sed/heredocs/scripts
+  never reaches the PreToolUse hook, so this one diffs the working tree after
+  every Bash call (per-session path+blob snapshot; one `git status` when
+  nothing changed) and runs the same arms on the definitions just written,
+  through the same endpoint and the same dedup channels. `additionalContext`
+  only; silent on any failure. The extractor, the prose/data skip list and the
+  local by-name duplicate arm are shared in `hooks/scribe_defs.sh`.
 - `skills/` → the universal process-skills, surfaced by description match.
 - `hooks/scribe_sync_processes.sh` (a 2nd SessionStart hook) + the `/scribe:sync`
  command → generate `~/.claude/skills/scribe-proc-*` stubs from your Scribe
@@ -34,6 +34,17 @@
          }
        ]
      }
+    ],
+    "PostToolUse": [
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "bash \"${CLAUDE_PLUGIN_ROOT}/hooks/scribe_after_write.sh\""
+          }
+        ]
+      }
    ]
  }
 }
@@ -0,0 +1,221 @@
+#!/usr/bin/env bash
+# Scribe plugin — PostToolUse write-path trigger on Bash (#2901).
+#
+# scribe_prior_art.sh fires before a Write/Edit TOOL CALL. Code written any
+# other way — sed, heredocs, python edit scripts, `cat > file` — never reached
+# it, so a whole class of edits (the ones a long session makes most) got no
+# prior-art hint, no ledger feed and no duplicate-family warning. This hook
+# closes that: after EVERY Bash call it asks git what changed in the working
+# tree since it last looked, and runs the same arms on the definitions that
+# were just written — the local by-name duplicate arm, the recorded prior-art
+# arms and the ledger's derive/divergence checks (#2900/#2793), via the same
+# /api/plugin/prior-art endpoint the pre-write hook uses.
+#
+# Post-hoc by a few seconds, in the same moment and the same session: "the
+# copy just landed; here is its family" — not "an audit found it later".
+#
+# Cheap when nothing changed: one `git status`. State per session, beside the
+# pre-write hook's (its three dedup channels are SHARED, so a family named by
+# one hook is not named again by the other):
+#   ${TMPDIR:-/tmp}/scribe-afterwrite/<sid>.snap   path<TAB>blob-hash of every
+#                                                  dirty/untracked file last seen
+#   ${TMPDIR:-/tmp}/scribe-priorart/<sid>.*        the dedup channels
+#
+# NEVER BLOCKS. It returns `additionalContext` only (no decision — there is
+# nothing left to decide, the write already happened). Any failure —
+# unconfigured, unreachable, not a git repo, malformed — exits 0 in silence.
+#
+# Config (same as the other hooks):
+#   CLAUDE_PLUGIN_OPTION_API_ENDPOINT  base URL, no trailing slash
+#   CLAUDE_PLUGIN_OPTION_API_TOKEN     fmcp_ API key (sensitive)
+#   SCRIBE_URL / SCRIBE_TOKEN override for the settings.json dogfooding path.
+set -uo pipefail
+
+command -v jq  >/dev/null 2>&1 || exit 0
+command -v git >/dev/null 2>&1 || exit 0
+
+# shellcheck source=plugin/hooks/scribe_defs.sh
+. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"
+
+# PostToolUse delivers { session_id, cwd, tool_name, tool_input, tool_response }.
+event=$(cat 2>/dev/null || true)
+tool_name=$(printf '%s' "$event" | jq -r '.tool_name // empty' 2>/dev/null) || exit 0
+[ "$tool_name" = "Bash" ] || exit 0
+session_id=$(printf '%s' "$event" | jq -r '.session_id // empty' 2>/dev/null) || session_id=""
+event_cwd=$(printf '%s' "$event" | jq -r '.cwd // empty' 2>/dev/null) || event_cwd=""
+work_dir=${event_cwd:-${CLAUDE_PROJECT_DIR:-$PWD}}
+repo_root=$(git -C "$work_dir" rev-parse --show-toplevel 2>/dev/null) || exit 0
+[ -n "$repo_root" ] || exit 0
+
+safe_sid=$(printf '%s' "${session_id:-nosession}" | tr -c 'A-Za-z0-9._-' '_')
+snap_dir="${TMPDIR:-/tmp}/scribe-afterwrite"
+mkdir -p "$snap_dir" 2>/dev/null || true
+snap="$snap_dir/${safe_sid}.snap"
+
+# What is dirty now: every modified / added / untracked path, with the blob
+# hash of its working-tree content. Hash, not mtime: portable (no stat
+# flags), exact (a touch is not a change), and untracked files hash the same
+# way tracked ones do.
+current=""
+while IFS= read -r line; do
+  [ -n "$line" ] || continue
+  status=${line:0:2}
+  path=${line:3}
+  case "$status" in
+    D*|*D) continue ;;                       # a deletion defines nothing
+  esac
+  case "$path" in
+    *" -> "*) path=${path##* -> } ;;          # rename: the new name
+  esac
+  # Porcelain quotes paths with special characters; those are skipped rather
+  # than unquoted badly — a filename needing quotes is not where shapes live.
+  case "$path" in
+    \"*) continue ;;
+  esac
+  [ -f "$repo_root/$path" ] || continue
+  sha=$(git -C "$repo_root" hash-object -- "$path" 2>/dev/null) || continue
+  current="${current}${path}"$'\t'"${sha}"$'\n'
+done < <(git -C "$repo_root" status --porcelain --untracked-files=all 2>/dev/null)
+
+previous=""
+[ -f "$snap" ] && previous=$(cat "$snap" 2>/dev/null || true)
+first_run=0
+[ -f "$snap" ] || first_run=1
+# Write the new snapshot NOW, before anything can fail below — the next call
+# must compare against this tree, whatever happens to this one's hint.
+printf '%s' "$current" > "$snap" 2>/dev/null || true
+
+# Changed = a (path, hash) pair not in the previous snapshot. On the very
+# first call of a session there is no previous snapshot; rather than report
+# every pre-existing dirty file as "just written", take only files touched in
+# the last minute — the Bash call that just ran is the likely author.
+changed=""
+while IFS=$'\t' read -r path sha; do
+  [ -n "${path:-}" ] || continue
+  if [ "$first_run" = 1 ]; then
+    [ -n "$(find "$repo_root/$path" -mmin -1 2>/dev/null)" ] || continue
+  else
+    case "$previous" in
+      *"${path}"$'\t'"${sha}"*) continue ;;
+    esac
+  fi
+  scribe_skip_path "$path" && continue
+  changed="${changed}${path}"$'\n'
+done <<< "$current"
+[ -n "$changed" ] || exit 0
+
+url=${SCRIBE_URL:-${CLAUDE_PLUGIN_OPTION_API_ENDPOINT:-}}
+token=${SCRIBE_TOKEN:-${CLAUDE_PLUGIN_OPTION_API_TOKEN:-}}
+case "$url"   in *'${'*) url="" ;;  esac
+case "$token" in *'${'*) token="" ;; esac
+repo=$(git -C "$repo_root" remote get-url origin 2>/dev/null || true)
+repo_q=""
+if [ -n "$repo" ]; then
+  enc=$(printf '%s' "$repo" | jq -sRr '@uri' 2>/dev/null) || enc=""
+  [ -n "$enc" ] && repo_q="&repo=${enc}"
+fi
+
+# The dedup channels are the PRE-write hook's files, on purpose (see header).
+state_dir="${TMPDIR:-/tmp}/scribe-priorart"
+mkdir -p "$state_dir" 2>/dev/null || true
+idfile="$state_dir/${safe_sid}.ids"
+syncfile="$state_dir/${safe_sid}.sync.ids"
+derivefile="$state_dir/${safe_sid}.derive.ids"
+
+combined=""
+n_files=0
+while IFS= read -r rel_path; do
+  [ -n "${rel_path:-}" ] || continue
+  # A Bash call that rewrote many files is a refactor or a generator, not a
+  # shape being instantiated; four is enough to name what matters.
+  n_files=$((n_files + 1))
+  [ "$n_files" -le 4 ] || break
+  file_path="$repo_root/$rel_path"
+
+  # The code just written: the ADDED lines of the uncommitted diff for a
+  # tracked file (sed, not cut: this strips one marker char per line, it is
+  # not a payload cap), the whole file when untracked.
+  if git -C "$repo_root" ls-files --error-unmatch -- "$rel_path" >/dev/null 2>&1; then
+    code=$(git -C "$repo_root" diff -U0 -- "$rel_path" 2>/dev/null | grep '^+' | grep -v '^+++' | sed 's/^+//') || code=""
+  else
+    code=$(cat "$file_path" 2>/dev/null) || code=""
+  fi
+  [ -n "$code" ] || continue
+  names=$(printf '%s' "$code" | scribe_defs | sort -u | head -12) || names=""
+  # Nothing DEFINED in what was written (prose, data, a call-site edit) →
+  # nothing to say; the arms are about shapes.
+  [ -n "$names" ] || continue
+
+  local_lines=$(scribe_local_dups "$repo_root" "$rel_path" <<< "$names") || local_lines=""
+  local_context=""
+  if [ -n "$local_lines" ]; then
+    local_context="> Already defined elsewhere in this repo — \`${rel_path}\` (just written) adds another copy; check before keeping it (\`git grep\` shown; a nudge, not a gate):"$'\n'"${local_lines}"
+  fi
+
+  context=""
+  body=""
+  if [ -n "$url" ] && [ -n "$token" ]; then
+    q=$(printf '%s' "$code" | head -c 1200)
+    path_enc=$(printf '%s' "$rel_path" | jq -sRr '@uri' 2>/dev/null) || path_enc=""
+    code_enc=$(printf '%s' "$q" | jq -sRr '@uri' 2>/dev/null) || code_enc=""
+    shapes_q=""
+    enc=$(printf '%s\n' "$names" \
+      | awk -F'\t' 'NF>=2 {printf "%s%s:%s", (n++?",":""), $1, $2}' \
+      | jq -sRr '@uri' 2>/dev/null) || enc=""
+    [ -n "$enc" ] && shapes_q="&shapes=${enc}"
+    exclude_q=""; sync_exclude_q=""; derive_exclude_q=""
+    if [ -f "$idfile" ]; then
+      seen=$(tr '\n' ',' < "$idfile" 2>/dev/null | sed 's/,$//')
+      [ -n "$seen" ] && exclude_q="&exclude_ids=${seen}"
+    fi
+    if [ -f "$syncfile" ]; then
+      sync_seen=$(tr '\n' ',' < "$syncfile" 2>/dev/null | sed 's/,$//')
+      [ -n "$sync_seen" ] && sync_exclude_q="&exclude_sync_ids=${sync_seen}"
+    fi
+    if [ -f "$derivefile" ]; then
+      derive_seen=$(tr '\n' ',' < "$derivefile" 2>/dev/null | sed 's/,$//' | jq -sRr '@uri' 2>/dev/null) || derive_seen=""
+      [ -n "$derive_seen" ] && derive_exclude_q="&exclude_derive=${derive_seen}"
+    fi
+    if [ -n "$path_enc" ]; then
+      body=$(curl -fsS --max-time 4 \
+        -H "Authorization: Bearer ${token}" \
+        "${url%/}/api/plugin/prior-art?path=${path_enc}&code=${code_enc}${repo_q}${exclude_q}${sync_exclude_q}${derive_exclude_q}${shapes_q}" 2>/dev/null) || body=""
+    fi
+    if [ -n "$body" ]; then
+      context=$(printf '%s' "$body" | jq -r '.context // empty' 2>/dev/null) || context=""
+      if [ -n "$context" ]; then
+        printf '%s' "$body" | jq -r '((.note_ids // []) - (.sync_note_ids // []))[]?' 2>/dev/null >> "$idfile" || true
+        printf '%s' "$body" | jq -r '(.sync_note_ids // [])[]?' 2>/dev/null >> "$syncfile" || true
+        printf '%s' "$body" | jq -r '(.derive_keys // [])[]?' 2>/dev/null >> "$derivefile" || true
+        # Several files in one call may name the same family: keep each
+        # token once, so the next request's exclude list stays exact.
+        for f in "$idfile" "$syncfile" "$derivefile"; do
+          [ -s "$f" ] && { sort -u -o "$f" "$f" 2>/dev/null || true; }
+        done
+      fi
+    fi
+  fi
+
+  # The record nudge (#2664), same gate as the pre-write hook: duplication
+  # demonstrated locally AND nothing recorded for it.
+  if [ -n "$local_lines" ]; then
+    n_recorded=$(printf '%s' "$body" | jq -r '.note_ids | length' 2>/dev/null) || n_recorded=0
+    if [ "${n_recorded:-0}" = "0" ] || [ "$n_recorded" = "" ]; then
+      local_context="${local_context}"$'\n'"> None of those existing copies is recorded in Scribe. If the version just written is the canonical one — or this edit is consolidating the copies — record it now with create_snippet so the next session is offered it instead of writing another copy."
+    fi
+  fi
+
+  part="$local_context"
+  if [ -n "$context" ]; then
+    [ -n "$part" ] && part="${part}"$'\n'
+    part="${part}${context}"
+  fi
+  [ -n "$part" ] || continue
+  [ -n "$combined" ] && combined="${combined}"$'\n'
+  combined="${combined}${part}"
+done <<< "$changed"
+
+[ -n "$combined" ] || exit 0
+jq -n --arg c "$combined" \
+  '{hookSpecificOutput: {hookEventName: "PostToolUse", additionalContext: $c}}'
+exit 0
@@ -0,0 +1,109 @@
+#!/usr/bin/env bash
+# shellcheck shell=bash
+# Scribe plugin — the pieces the two write-path hooks share (#2901).
+#
+# scribe_prior_art.sh fires BEFORE a Write/Edit tool call; scribe_after_write.sh
+# fires AFTER a Bash tool call and diffs the working tree, so code written by
+# sed/heredocs/scripts gets the same prior-art and ledger checks. Both need the
+# same three things, kept here so they cannot drift apart:
+#
+#   scribe_skip_path PATH      formats that hold prose or data, not shapes
+#   scribe_defs                stdin code → "kind<TAB>name" per definition
+#   scribe_local_dups ROOT REL "kind<TAB>name" lines on stdin → the by-name
+#                              local-duplicate lines (ARM 1, #2280)
+#
+# Sourced, not executed: `. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"`.
+
+# Skip formats that hold prose or data rather than reusable code. Purely to
+# avoid a pointless round-trip — the server would return nothing for these
+# anyway. Config formats are NOT skipped: a CI workflow or a compose file is
+# often exactly the thing worth reusing.
+scribe_skip_path() {
+  case "$1" in
+    *.md|*.mdx|*.txt|*.rst|*.json|*.lock|*.log|*.csv|*.tsv|*.svg|*.png|*.jpg|*.jpeg|*.gif|*.ico|*.pdf)
+      return 0 ;;
+  esac
+  return 1
+}
+
+# ---------------------------------------------------------------------------
+# kind<TAB>name for each thing a piece of code DEFINES, in source order. One
+# program, two consumers: the local duplicate arm (every definition in the
+# payload) and the ledger feed (#2791, below: the definitions being written,
+# or the one enclosing an Edit). Rule-for-rule mirrored by the server's
+# services/coverage.py extract_shapes — ledger rows are keyed by what THAT
+# sees, so the two must agree on what counts as a definition.
+scribe_defs() {
+  awk '
+    {
+      # CSS class definition: .name { or .name,
+      if (match($0, /^[[:space:]]*\.[A-Za-z][A-Za-z0-9_-]*[[:space:]]*[,{]/)) {
+        t = $0; sub(/^[[:space:]]*\./, "", t); sub(/[[:space:]]*[,{].*$/, "", t)
+        if (t != "") print "css\t" t; next
+      }
+      line = $0; sub(/^[[:space:]]+/, "", line)
+      # Strip leading declaration modifiers so the definition keyword is the
+      # first word regardless of language (export/pub/private/suspend/...).
+      sub(/^((pub(\([a-z]+\))?|export|default|private|internal|protected|public|static|suspend|async|open|sealed|data|abstract|final|inline|unsafe|extern|override)[[:space:]]+)*/, "", line)
+      # Go method with receiver: func (r *T) Name(
+      if (match(line, /^func[[:space:]]*\([^)]*\)[[:space:]]*[A-Za-z_]/)) {
+        t = line; sub(/^func[[:space:]]*\([^)]*\)[[:space:]]*/, "", t)
+        sub(/[^A-Za-z0-9_].*$/, "", t)
+        if (t != "") print "sym\t" t; next
+      }
+      # Keyword-announced definitions, functions and named types alike.
+      # Dunders are skipped: every class defines __init__, so "already defined
+      # in N other files" is guaranteed noise for them — and noise is what
+      # teaches sessions to skip the hint.
+      if (match(line, /^(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+[A-Za-z_$]/)) {
+        t = line; sub(/^[a-z]+[[:space:]]+/, "", t)
+        sub(/[^A-Za-z0-9_$].*$/, "", t)
+        if (t != "" && t !~ /^__.*__$/) print "sym\t" t; next
+      }
+      # Arrow/expression assignment: const name = (…) / let name = async (
+      if (match(line, /^(const|let)[[:space:]]+[A-Za-z_$][A-Za-z0-9_$]*[[:space:]]*=[[:space:]]*(async[[:space:]]*)?[(<]/)) {
+        t = line; sub(/^(const|let)[[:space:]]+/, "", t)
+        sub(/[^A-Za-z0-9_$].*$/, "", t)
+        if (t != "") print "sym\t" t; next
+      }
+    }
+  ' 2>/dev/null
+}
+
+
+# ---------------------------------------------------------------------------
+# ARM 1 — BY NAME, LOCALLY (#2280). Does a definition of this already exist?
+#
+# The recorded arms ask Scribe what was RECORDED; the ledger arm (#2900) asks
+# what a BOUND repo's ledger knows. A helper nobody recorded, in a repo nobody
+# bound, is invisible to both — which is how `.btn-primary` came to be defined
+# four times, already diverged. This arm asks the one question only the
+# developer's machine can answer, inside the repo, holding the code about to
+# be written: no index, no storage, no server — it runs even on an install
+# that has never configured Scribe.
+#
+# Definition-shaped patterns only. Grepping for bare occurrences would match
+# every CALL site and drown the real finding — and a hint that is mostly noise
+# is one people learn to skip, which is worse than none. ALL code, not a
+# language shortlist (#2682): the same keyword family scribe_defs announces.
+#
+# $1 repo root, $2 repo-relative path of the file being written (excluded from
+# the grep — it would always match itself on an Edit). Definitions on stdin.
+# Prints one "> - `name` is already defined in N other file(s): …" per hit.
+scribe_local_dups() {
+  local root="$1" rel="$2" kind name pat hits count label files
+  while IFS=$'\t' read -r kind name; do
+    [ -n "${name:-}" ] || continue
+    case "$kind" in
+      css) pat="^[[:space:]]*\.${name}[[:space:]]*[,{]" ;;
+      *)   pat="(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+${name}[^A-Za-z0-9_]|func[[:space:]]*\([^)]*\)[[:space:]]*${name}[[:space:]]*\(|(const|let)[[:space:]]+${name}[[:space:]]*=" ;;
+    esac
+    # -I skips binaries; :(exclude) drops the file being written.
+    hits=$(git -C "$root" grep -I -l -E -e "$pat" -- . ":(exclude)${rel}" 2>/dev/null | head -4) || hits=""
+    [ -n "$hits" ] || continue
+    count=$(printf '%s\n' "$hits" | grep -c . 2>/dev/null || echo 0)
+    label=$([ "$kind" = css ] && printf '.%s' "$name" || printf '%s' "$name")
+    files=$(printf '%s' "$hits" | tr '\n' ' ' | sed 's/ $//')
+    printf '> - `%s` is already defined in %s other file(s): %s\n' "$label" "$count" "$files"
+  done
+}
@@ -51,14 +51,12 @@ code=$(printf '%s' "$event" | jq -r '
  .tool_input.content // .tool_input.file_content //
  .tool_input.new_string // .tool_input.new_str // empty' 2>/dev/null) || code=""

-# Skip formats that hold prose or data rather than reusable code. Purely to
-# avoid a pointless round-trip — the server would return nothing for these
-# anyway. Config formats are NOT skipped: a CI workflow or a compose file is
-# often exactly the thing worth reusing.
-case "$file_path" in
-  *.md|*.mdx|*.txt|*.rst|*.json|*.lock|*.log|*.csv|*.tsv|*.svg|*.png|*.jpg|*.jpeg|*.gif|*.ico|*.pdf)
-    exit 0 ;;
-esac
+# Shared with the after-write hook (#2901): the prose/data skip list, the
+# definition extractor and the local by-name duplicate arm live in
+# scribe_defs.sh so the two hooks cannot drift apart.
+# shellcheck source=plugin/hooks/scribe_defs.sh
+. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"
+scribe_skip_path "$file_path" && exit 0

 # Snippet locations are recorded repo-relative, so send a repo-relative path —
 # an absolute one would simply match nothing. Resolved BEFORE the config gate
@@ -73,78 +71,8 @@ if [ -n "$repo_root" ]; then
  esac
 fi

-# ---------------------------------------------------------------------------
-# ARM 1 — BY NAME, LOCALLY (#2280). Does a definition of this already exist?
-#
-# The other two arms ask Scribe what was RECORDED. Scribe has never read a line
-# of the codebase, so a helper nobody thought to record is invisible to them —
-# which is how `.btn-primary` came to be defined four times, in four scoped
-# stylesheets, already diverged. It was never a snippet, so no threshold and no
-# query rewrite could ever have surfaced it.
-#
-# This arm closes that by asking the only question the record cannot answer,
-# in the only place that can: the hook already runs on the developer's machine,
-# inside the repo, holding the code about to be written. No index, no storage,
-# no staleness, and no server — it deliberately runs even on an install that
-# has never configured Scribe.
-#
-# Definition-shaped patterns only. Grepping for bare occurrences would match
-# every CALL site and drown the real finding — and a hint that is mostly noise
-# is one people learn to skip, which is worse than none.
-#
-# ALL code, not a language shortlist (#2682): the detector was born covering
-# only the languages of the repo it was written in, which silently amputated
-# this whole arm — and the record nudge gated on it — for every Go/Kotlin/Rust
-# project. Definitions are announced by a small keyword family across
-# languages (func/fun/fn/function/def/sub · class/struct/trait/interface/
-# enum/object/protocol/type), so one modifier-strip + keyword match covers
-# them all. Known out of scope: keyword-less declaration syntax (C/Java/Dart
-# `ReturnType name(...)`) needs a real parser, and `impl` blocks are excluded
-# because several per type is normal Rust, not duplication.
-# ---------------------------------------------------------------------------
-# kind<TAB>name for each thing a piece of code DEFINES, in source order. One
-# program, two consumers: the local duplicate arm (every definition in the
-# payload) and the ledger feed (#2791, below: the definitions being written,
-# or the one enclosing an Edit). Rule-for-rule mirrored by the server's
-# services/coverage.py extract_shapes — ledger rows are keyed by what THAT
-# sees, so the two must agree on what counts as a definition.
-scribe_defs() {
-  awk '
-    {
-      # CSS class definition: .name { or .name,
-      if (match($0, /^[[:space:]]*\.[A-Za-z][A-Za-z0-9_-]*[[:space:]]*[,{]/)) {
-        t = $0; sub(/^[[:space:]]*\./, "", t); sub(/[[:space:]]*[,{].*$/, "", t)
-        if (t != "") print "css\t" t; next
-      }
-      line = $0; sub(/^[[:space:]]+/, "", line)
-      # Strip leading declaration modifiers so the definition keyword is the
-      # first word regardless of language (export/pub/private/suspend/...).
-      sub(/^((pub(\([a-z]+\))?|export|default|private|internal|protected|public|static|suspend|async|open|sealed|data|abstract|final|inline|unsafe|extern|override)[[:space:]]+)*/, "", line)
-      # Go method with receiver: func (r *T) Name(
-      if (match(line, /^func[[:space:]]*\([^)]*\)[[:space:]]*[A-Za-z_]/)) {
-        t = line; sub(/^func[[:space:]]*\([^)]*\)[[:space:]]*/, "", t)
-        sub(/[^A-Za-z0-9_].*$/, "", t)
-        if (t != "") print "sym\t" t; next
-      }
-      # Keyword-announced definitions, functions and named types alike.
-      # Dunders are skipped: every class defines __init__, so "already defined
-      # in N other files" is guaranteed noise for them — and noise is what
-      # teaches sessions to skip the hint.
-      if (match(line, /^(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+[A-Za-z_$]/)) {
-        t = line; sub(/^[a-z]+[[:space:]]+/, "", t)
-        sub(/[^A-Za-z0-9_$].*$/, "", t)
-        if (t != "" && t !~ /^__.*__$/) print "sym\t" t; next
-      }
-      # Arrow/expression assignment: const name = (…) / let name = async (
-      if (match(line, /^(const|let)[[:space:]]+[A-Za-z_$][A-Za-z0-9_$]*[[:space:]]*=[[:space:]]*(async[[:space:]]*)?[(<]/)) {
-        t = line; sub(/^(const|let)[[:space:]]+/, "", t)
-        sub(/[^A-Za-z0-9_$].*$/, "", t)
-        if (t != "") print "sym\t" t; next
-      }
-    }
-  ' 2>/dev/null
-}
-
+# ARM 1 — BY NAME, LOCALLY (#2280): does a definition of this already exist
+# in the repo? (scribe_local_dups in scribe_defs.sh carries the why.)
 names=""
 if [ -n "$code" ]; then
  names=$(printf '%s' "$code" | scribe_defs | sort -u | head -12) || names=""
@@ -152,21 +80,8 @@ fi

 local_lines=""
 if [ -n "$repo_root" ] && [ -n "$names" ]; then
-  while IFS=$'\t' read -r kind name; do
-    [ -n "${name:-}" ] || continue
-    case "$kind" in
-      css) pat="^[[:space:]]*\.${name}[[:space:]]*[,{]" ;;
-      *)   pat="(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+${name}[^A-Za-z0-9_]|func[[:space:]]*\([^)]*\)[[:space:]]*${name}[[:space:]]*\(|(const|let)[[:space:]]+${name}[[:space:]]*=" ;;
-    esac
-    # -I skips binaries; :(exclude) drops the file being written, which would
-    # otherwise always match itself on an Edit.
-    hits=$(git -C "$repo_root" grep -I -l -E -e "$pat" -- . ":(exclude)${rel_path}" 2>/dev/null | head -4) || hits=""
-    [ -n "$hits" ] || continue
-    count=$(printf '%s\n' "$hits" | grep -c . 2>/dev/null || echo 0)
-    label=$([ "$kind" = css ] && printf '.%s' "$name" || printf '%s' "$name")
-    files=$(printf '%s' "$hits" | tr '\n' ' ' | sed 's/ $//')
-    local_lines="${local_lines}> - \`${label}\` is already defined in ${count} other file(s): ${files}"$'\n'
-  done <<< "$names"
+  local_lines=$(scribe_local_dups "$repo_root" "$rel_path" <<< "$names") || local_lines=""
+  [ -n "$local_lines" ] && local_lines="${local_lines}"$'\n'
 fi

 local_context=""
@@ -258,14 +173,22 @@ fi
 # the sync nudge when the recorded file itself is edited later.
 state_dir="${TMPDIR:-/tmp}/scribe-priorart"
 mkdir -p "$state_dir" 2>/dev/null || true
+#
+# A THIRD channel (#2900): the ledger's derive arm names a duplicate family
+# (a derive group id) or a canon elsewhere (`canon:<snippet_id>`) for the
+# shapes being written. Keyed by that token, not a note id, so it dedups on
+# its own file and a family is named once per session, not at every edit.
 idfile=""
 syncfile=""
+derivefile=""
 exclude_q=""
 sync_exclude_q=""
+derive_exclude_q=""
 if [ -n "$session_id" ]; then
  safe_sid=$(printf '%s' "$session_id" | tr -c 'A-Za-z0-9._-' '_')
  idfile="$state_dir/${safe_sid}.ids"
  syncfile="$state_dir/${safe_sid}.sync.ids"
+  derivefile="$state_dir/${safe_sid}.derive.ids"
  if [ -f "$idfile" ]; then
    seen=$(tr '\n' ',' < "$idfile" 2>/dev/null | sed 's/,$//')
    [ -n "$seen" ] && exclude_q="&exclude_ids=${seen}"
@@ -274,13 +197,17 @@ if [ -n "$session_id" ]; then
    sync_seen=$(tr '\n' ',' < "$syncfile" 2>/dev/null | sed 's/,$//')
    [ -n "$sync_seen" ] && sync_exclude_q="&exclude_sync_ids=${sync_seen}"
  fi
+  if [ -f "$derivefile" ]; then
+    derive_seen=$(tr '\n' ',' < "$derivefile" 2>/dev/null | sed 's/,$//' | jq -sRr '@uri' 2>/dev/null) || derive_seen=""
+    [ -n "$derive_seen" ] && derive_exclude_q="&exclude_derive=${derive_seen}"
+  fi
 fi

 # `|| true`, not `|| exit 0`: an unreachable instance must not discard a local
 # finding that needed no instance to produce.
 body=$(curl -fsS --max-time 5 \
  -H "Authorization: Bearer ${token}" \
-  "${url%/}/api/plugin/prior-art?path=${path_enc}&code=${code_enc}${repo_q}${exclude_q}${sync_exclude_q}${shapes_q}" 2>/dev/null) || body=""
+  "${url%/}/api/plugin/prior-art?path=${path_enc}&code=${code_enc}${repo_q}${exclude_q}${sync_exclude_q}${derive_exclude_q}${shapes_q}" 2>/dev/null) || body=""

 context=""
 if [ -n "$body" ]; then
@@ -295,6 +222,9 @@ if [ -n "$body" ]; then
    if [ -n "$syncfile" ]; then
      printf '%s' "$body" | jq -r '(.sync_note_ids // [])[]?' 2>/dev/null >> "$syncfile" || true
    fi
+    if [ -n "$derivefile" ]; then
+      printf '%s' "$body" | jq -r '(.derive_keys // [])[]?' 2>/dev/null >> "$derivefile" || true
+    fi
  fi
 fi

@@ -66,7 +66,10 @@ for the operator's work, and as your own working memory across sessions.
  should read as a map of every shape in it. The backstop still holds:
  noticing the second copy of anything, or consolidating copies into a shared
  X, means X gets recorded before that work is finished — which is how a
-  codebase is kept from growing four `.btn-primary` definitions.
+  codebase is kept from growing four `.btn-primary` definitions. The write-path
+  hooks (before a Write/Edit, and after any Bash call that changed the tree)
+  name a known duplicate family or a canon elsewhere for what was just
+  written — act on that line at the write, not at the next audit.
 - Do **not** keep the operator's rules, plans, or project notes in local
  memory / CLAUDE.md in parallel with Scribe — Scribe holds the single copy.
 - **Compact at clean seams** — because you record as you go, a context
@@ -44,6 +44,13 @@ through recall/auto-inject; this skill is the active reflex around that.
  it before you go any further. Either it's the helper you were about to
  duplicate — reuse it and drop yours — or it isn't, and the record needs the new
  location adding. Both are cheaper now than after the duplicate settles in.
+- **A `Shape ledger at …` line is the ledger speaking, not the record.** It
+  names a duplicate family ("identical body in N other files, no canon") or a
+  canon elsewhere for a name you just wrote — for edits made through Bash
+  (sed, heredocs, scripts) as much as through Write/Edit. Derive the family or
+  reuse the canon *now*; a family that is convention rather than copies is
+  dismissed with `classify_shapes(..., status="exempt",
+  reason_code="convention-plumbing")`, never ignored.
 - **A `[records this file]` hint is a duty, not a menu.** When the hint says a
  snippet records the very file you're editing, the record's freshness is now
  YOUR edit's responsibility: if the edit changes the recorded shape,
@@ -85,6 +85,34 @@ the dominant form, `create_snippet` it, migrate the outliers, then classify
 the rest as instances. Canon is determined from the code; consistency comes
 from the derivation, not from asking permission.

+## Derive groups are drift, not audit material
+
+The catalogue exists so the codebase is DRY **from inception**, not as DRY as
+the last sweep left it. Three surfaces say so without anyone running an audit
+(milestone 299):
+
+- **At the write** — the prior-art hint (the Write/Edit hook, and since
+  0.1.39 the after-write hook on Bash, so sed/heredoc/script edits count too)
+  carries a `Shape ledger at <path>` line when a name just written is a known
+  **duplicate family** ("identical body in N other files, no canon") or a
+  **canon elsewhere** ("snippet #N at <path> — reuse, don't redefine"). Act
+  on it *then*: pull the canon and build from it, or derive the family now —
+  `create_snippet` the dominant form, repoint the copies, `classify_shapes`
+  them `instance`. A family is named once per session.
+- **On arrival** — the coverage line's `standing:` block (shown even when
+  nothing is unclassified) and `derive_new` ("+N new copies since last
+  refresh: .x in <path>") name what drifted since the previous refresh. That
+  is the todo of the moment, sized to the last batch — not a backlog.
+- **A family that is convention, not copies** — component-local `load` /
+  `toggle` / `save` that happen to share a name — is dismissed, not
+  consolidated: `classify_shapes(..., status="exempt",
+  reason_code="convention-plumbing", reason=…)` (or `classify_shapes_by_rule`
+  for a whole family) removes it from the queue. Dismissal is a judgment and
+  it is recorded; silence is not.
+
+After the one-time pay-down the derive queue reads empty; anything in it
+afterwards is drift of the moment, and the hint already said so at the write.
+
 ## The divergence readout — button B where button A is canon

 Three questions the ledger answers mechanically (#2793):
@@ -203,6 +203,17 @@ SMOKE_EVENTS: dict[str, str] = {
    ),
    "scribe_sync_processes.sh": json.dumps({"source": "startup"}),
    "scribe_session_context.sh": json.dumps({"source": "startup"}),
+    # The after-write hook (#2901) diffs the working tree; on CI's clean
+    # checkout there is nothing to report, so silence is the right assertion.
+    # (On a dirty local tree with a definition just written it may speak —
+    # that is the hook working, not a failure of the contract.)
+    "scribe_after_write.sh": json.dumps(
+        {"session_id": "smoke", "cwd": ".", "tool_name": "Bash",
+         "tool_input": {"command": "true"}, "tool_response": {}}
+    ),
+    # The shared library is sourced, never run; executed bare it defines
+    # functions and exits — silent by construction.
+    "scribe_defs.sh": "",
 }

 # The one hook that legitimately produces output with no credentials.
@@ -295,7 +295,9 @@ async def refresh_pattern_coverage(project_id: int) -> dict:
    Returns the accounting payload — total, accounted, counts by status,
    unclassified, repos, largest_gaps, `proposed` (canon proposals awaiting
    confirmation), `derive_groups` (the biggest repeats-with-no-canon
-    families), `proposer` (what this refresh examined) — plus
+    families), `derive_new` (copies that joined a family since the previous
+    refresh — the drift to act on now: derive the canon, don't queue an
+    audit), `proposer` (what this refresh examined) — plus
    `pattern_coverage`, the same one-line summary enter_project carries.
    """
    uid = current_user_id()
@@ -129,6 +129,10 @@ async def write_path_prior_art():
                             surfaced. A separate channel on purpose: a reuse
                             hint shown early must not suppress the record-sync
                             nudge when the recorded file is edited later.
+        exclude_derive (opt) — comma-separated derive keys (a derive group id
+                             or `canon:<snippet_id>`) already named this
+                             session by the ledger arm (#2900); its own
+                             channel, like the two above.
        shapes (opt)       — comma-separated `kind:name` definitions the hook
                             found in (or enclosing) the payload, kind being
                             css|sym. The shape ledger's write-path feed
@@ -144,6 +148,9 @@ async def write_path_prior_art():
    project_id, repo, _unbound = await _project_scope()
    exclude_ids = _int_list(request.args.get("exclude_ids"))
    exclude_sync_ids = _int_list(request.args.get("exclude_sync_ids"))
+    exclude_derive = [
+        p.strip() for p in (request.args.get("exclude_derive") or "").split(",") if p.strip()
+    ]
    shapes = _parse_shapes(request.args.get("shapes") or "")
    api_key = getattr(g, "api_key", None)
    may_stamp = api_key is None or getattr(api_key, "scope", "") == "write"
@@ -153,6 +160,7 @@ async def write_path_prior_art():
        exclude_ids=exclude_ids, exclude_sync_ids=exclude_sync_ids,
        stamp_shapes=shapes if may_stamp else None,
        repo_key=repo_bindings_svc.normalize_repo_key(repo) if repo else "",
+        exclude_derive=exclude_derive,
    )
    return jsonify(result)

@@ -462,15 +462,20 @@ async def compute_coverage(
        await shape_ledger.apply_derive_groups(project_id)
    except Exception:
        logger.warning("derive-first grouping failed", exc_info=True)
-    # The button-B pass (#2793): shapes new since the PREVIOUS computation,
-    # where a canon dominates. The previous computation's stamp is the cache;
-    # a first seed has none, so it flags nothing (everything is new then).
+    # "Since the previous computation" — the cache's stamp. A first seed has
+    # none, so nothing is new then. Read once; two passes use it: the
+    # button-B flag (#2793) and the derive-new drift count (#2899).
+    since = None
    try:
        previous = await get_setting(user_id, f"{_CACHE_KEY_PREFIX}{project_id}")
-        since = None
        if previous:
            stamp = (json.loads(previous) or {}).get("computed_at")
            since = datetime.fromisoformat(stamp) if stamp else None
+    except Exception:
+        logger.warning("previous coverage stamp unreadable", exc_info=True)
+    # The button-B pass (#2793): shapes new since the PREVIOUS computation,
+    # where a canon dominates.
+    try:
        await shape_ledger.flag_divergence(project_id, since=since)
    except Exception:
        logger.warning("divergence pass failed", exc_info=True)
@@ -491,6 +496,7 @@ async def compute_coverage(
    unclassified = counts.pop("unclassified")
    proposals = shape_ledger.proposal_summary(rows)
    divergence = shape_ledger.divergence_summary(rows)
+    derive_new = shape_ledger.derive_new_summary(rows, since=since)
    return {
        "total": len(rows),
        "accounted": len(rows) - unclassified,
@@ -501,6 +507,10 @@ async def compute_coverage(
        "proposed": proposals["proposed"],
        "derive_groups": proposals["derive_groups"],
        "top_canon": proposals.get("top_canon"),
+        # Drift since the previous refresh (#2899): copies that joined a
+        # duplicate family — what the arrival line names so drift is noticed
+        # on entering, not found by an audit.
+        "derive_new": derive_new,
        "proposer": proposer_stats,
        # The divergence readout (#2793): button B where button A is canon,
        # and judged shapes whose bodies moved since they were judged.
@@ -648,29 +658,46 @@ def coverage_line(coverage: dict) -> str:
        line += f" — {breakdown}"
    line += f" (estimate{', computed ' + day if day else ''})"
    unclassified = coverage.get("unclassified", 0)
+    # The standing work, built whatever the todo count (#2899). Since the
+    # scoped bucket (#2869) a ledger can read 100% accounted and still carry
+    # derive groups, proposals and divergence; gating this block on
+    # `unclassified > 0` is how 439 derive rows went unmentioned.
+    standing = []
+    if coverage.get("proposed"):
+        standing.append(f"{coverage['proposed']} proposed")
+    n_groups = len(coverage.get("derive_groups") or [])
+    if n_groups:
+        standing.append(f"{n_groups} derive group{'s' if n_groups != 1 else ''}")
+    # Drift since the previous refresh: copies that joined a family, the
+    # first one named — the sentence the arrival moment exists to say.
+    new = coverage.get("derive_new") or {}
+    if new.get("count"):
+        n = new["count"]
+        first_new = (new.get("examples") or [{}])[0]
+        where = (
+            f": {first_new['label']} in {first_new['path']}"
+            if first_new.get("label") and first_new.get("path") else ""
+        )
+        standing.append(f"+{n} new cop{'y' if n == 1 else 'ies'} since last refresh{where}")
+    if coverage.get("divergent"):
+        standing.append(f"{coverage['divergent']} DIVERGENT")
+    # The next action, on the line (#2874): the canon with the biggest
+    # queue to confirm, and the widest body-identical copy to consolidate.
+    top = coverage.get("top_canon") or {}
+    if top.get("snippet_id"):
+        standing.append(f"top canon #{top['snippet_id']} ×{top.get('count', 0)}")
+    first = (coverage.get("derive_groups") or [{}])[0]
+    if first.get("label") and first.get("files"):
+        standing.append(f"top copy {first['label']} ×{first['files']} files")
    if unclassified:
        line += f"; {unclassified} unclassified"
-        standing = []
-        if coverage.get("proposed"):
-            standing.append(f"{coverage['proposed']} proposed")
-        n_groups = len(coverage.get("derive_groups") or [])
-        if n_groups:
-            standing.append(f"{n_groups} derive group{'s' if n_groups != 1 else ''}")
-        if coverage.get("divergent"):
-            standing.append(f"{coverage['divergent']} DIVERGENT")
-        # The next action, on the line (#2874): the canon with the biggest
-        # queue to confirm, and the widest body-identical copy to consolidate.
-        top = coverage.get("top_canon") or {}
-        if top.get("snippet_id"):
-            standing.append(f"top canon #{top['snippet_id']} ×{top.get('count', 0)}")
-        first = (coverage.get("derive_groups") or [{}])[0]
-        if first.get("label") and first.get("files"):
-            standing.append(f"top copy {first['label']} ×{first['files']} files")
        if standing:
            line += f" ({', '.join(standing)})"
        gaps = [g["dir"] for g in coverage.get("largest_gaps") or []]
        if gaps:
            line += ", largest: " + ", ".join(gaps)
+    elif standing:
+        line += f"; standing: {', '.join(standing)}"
    if coverage.get("recheck"):
        line += f"; {coverage['recheck']} judged shape{'s' if coverage['recheck'] != 1 else ''} changed since judged — recheck"
    return line
@@ -706,6 +706,7 @@ async def build_write_path_hint(
    exclude_sync_ids: list[int] | None = None,
    stamp_shapes: list[tuple[str, str]] | None = None,
    repo_key: str = "",
+    exclude_derive: list[str] | None = None,
 ) -> dict:
    """Prior-art hint for the plugin's PreToolUse hook on Write/Edit.

@@ -765,7 +766,7 @@ async def build_write_path_hint(
    """
    cfg = await get_writepath_config(user_id)
    empty = {"context": "", "note_ids": [], "sync_note_ids": [], "config": cfg,
-             "stamped": [], "divergence": []}
+             "stamped": [], "divergence": [], "derive": [], "derive_keys": []}
    path = (path or "").strip()
    if not cfg["enabled"] or not path:
        return empty
@@ -935,7 +936,20 @@ async def build_write_path_hint(
            )
        except Exception:
            logger.warning("write-time divergence check failed", exc_info=True)
-    if not synced and not menu and not stamped and not divergence:
+    # The in-band DERIVE check (#2900): the ledger's own knowledge of the
+    # names being written — a duplicate family with no canon, or a canon
+    # recorded elsewhere. This is the arm the by-name local grep could not
+    # be: it knows whether the other copies are canon or stray. Keyed per
+    # session (`exclude_derive`) so a family is named once, not per edit.
+    derive: list[dict] = []
+    if stamp_shapes and project_id:
+        try:
+            found = await shape_ledger_svc.write_time_derive(project_id, path, stamp_shapes)
+            skip = set(exclude_derive or [])
+            derive = [d for d in found if d.get("key") not in skip]
+        except Exception:
+            logger.warning("write-time derive check failed", exc_info=True)
+    if not synced and not menu and not stamped and not divergence and not derive:
        return empty

    owners = await owner_names_for({
@@ -1003,6 +1017,8 @@ async def build_write_path_hint(
        lines.append(_stamp_line(path, stamped))
    if divergence:
        lines.append(_divergence_line(path, divergence))
+    if derive:
+        lines.append(_derive_line(path, derive))

    # Split by arm, which is the whole reason this table exists. The place arm
    # carries no score and so has no home in retrieval_logs; before #2085 a
@@ -1027,9 +1043,40 @@ async def build_write_path_hint(
        "config": cfg,
        "stamped": stamped,
        "divergence": divergence,
+        "derive": derive,
+        "derive_keys": [d["key"] for d in derive],
    }


+def _derive_line(path: str, derive: list[dict]) -> str:
+    """The ledger's word on the names being written (#2900): a duplicate
+    family to derive, or a canon to reuse — said at the write."""
+    parts = []
+    for d in derive:
+        if d.get("canon"):
+            c = d["canon"]
+            parts.append(
+                f"`{c['label']}` is canon — snippet #{c['snippet_id']} at `{c['path']}`; "
+                "pull it and reuse, don't redefine"
+            )
+            continue
+        f = d["family"]
+        how = "identical body" if f.get("identical") else "same name defined"
+        files = ", ".join(f"`{x}`" for x in f.get("files") or [])
+        more = f.get("file_count", 0) - len(f.get("files") or [])
+        if more > 0:
+            files += f" +{more} more"
+        parts.append(
+            f"`{f['label']}` is a duplicate family with no canon — {how} in "
+            f"{f.get('file_count', 0)} other file(s): {files}; derive it now: "
+            "record the canon (create_snippet) and make the copies instances "
+            "(classify_shapes) — or, if these are convention not copies, "
+            "`classify_shapes(..., status=\"exempt\", reason_code=\"convention-plumbing\")` "
+            "dismisses the family — rather than adding another copy"
+        )
+    return f"> Shape ledger at `{path}`: " + "; ".join(parts) + "."
+
+
 def _divergence_line(path: str, divergence: list[dict]) -> str:
    """Button B where button A is canon — named at the write (#2793)."""
    parts = [
@@ -1404,6 +1404,34 @@ def proposal_summary(rows: Iterable[CodeShape], *, top: int = 8) -> dict:
    return {"proposed": proposed, "derive_groups": ranked[:top], "top_canon": top_canon}


+def derive_new_summary(
+    rows: Iterable[CodeShape], *, since: datetime | None, top: int = 3
+) -> dict:
+    """The arrival-moment drift signal (#2899): derive-grouped rows FIRST
+    SEEN after ``since`` — the previous refresh's stamp, the same one
+    flag_divergence uses. "Since the last refresh, N more copies joined a
+    duplicate family" is the sentence that makes the derive queue a thing
+    you notice on entering, not a thing an audit finds. ``since`` None (a
+    first seed) means nothing is new. Judged rows never count."""
+    if since is None:
+        return {"count": 0, "examples": []}
+    fresh = [
+        r for r in rows
+        if r.proposal_basis == "derive" and r.proposal_group
+        and r.status in _MECHANICAL_TODO and r.vanished_at is None
+        and r.created_at is not None and r.created_at > since
+    ]
+    fresh.sort(key=lambda r: r.created_at, reverse=True)
+    return {
+        "count": len(fresh),
+        "examples": [
+            {"label": ("." if r.kind == "css" else "") + r.symbol,
+             "path": r.path, "group": r.proposal_group}
+            for r in fresh[:top]
+        ],
+    }
+
+
 async def confirm_proposals(
    user_id: int,
    project_id: int,
@@ -1566,6 +1594,75 @@ async def write_time_divergence(
    return out


+# How many other files a family line names before "…" — enough to go look,
+# not a wall.
+_DERIVE_FILES_SHOWN = 4
+
+
+async def write_time_derive(
+    project_id: int, path: str, shapes: list[tuple[str, str]]
+) -> list[dict]:
+    """The in-band DERIVE check (#2900): for each (kind, name) the hook
+    named at ``path``, what the ledger already knows about that name
+    elsewhere in the project —
+
+      family  the name sits in a derive-first group (identical body in N
+              files, or the same name in ≥3): "this is a known duplicate
+              family with no canon — derive it now, don't add a copy";
+      canon   a `canonical` row of that name at another path: "this is
+              canon #N at <path> — reuse, don't redefine".
+
+    Only for shapes not yet judged at ``path`` (a judged shape is not
+    re-litigated at every edit), never for the canon's own file. Returns
+    [{symbol, kind, key, family?|canon?}] — `key` is the dedup token the
+    hook keeps per session (the group id, or canon:<snippet_id>)."""
+    wanted = {(k, _norm_symbol(n)): n for k, n in shapes if n}
+    if not wanted:
+        return []
+    async with async_session() as session:
+        rows = (
+            await session.execute(
+                select(CodeShape).where(
+                    CodeShape.project_id == project_id,
+                    CodeShape.vanished_at.is_(None),
+                    CodeShape.symbol.in_({norm for (_k, norm) in wanted}),
+                )
+            )
+        ).scalars().all()
+    out: list[dict] = []
+    for (kind, norm), name in wanted.items():
+        same = [r for r in rows if r.kind == kind and _norm_symbol(r.symbol) == norm]
+        here = next((r for r in same if r.path == path), None)
+        if here is not None and here.status not in _MECHANICAL_TODO:
+            continue  # judged here (or this IS the canon): nothing to say
+        others = [r for r in same if r.path != path]
+        label = ("." if kind == "css" else "") + name
+        canon = next((r for r in others if r.status == "canonical" and r.snippet_id), None)
+        if canon is not None:
+            out.append({"symbol": name, "kind": kind, "key": f"canon:{canon.snippet_id}",
+                        "canon": {"snippet_id": canon.snippet_id, "path": canon.path,
+                                  "label": label}})
+            continue
+        grouped = [r for r in others if r.proposal_group and r.status in _MECHANICAL_TODO]
+        if here is not None and here.proposal_group:
+            grouped = [r for r in grouped if r.proposal_group == here.proposal_group] or grouped
+        if not grouped:
+            continue
+        group = grouped[0].proposal_group
+        members = [r for r in grouped if r.proposal_group == group]
+        files = sorted({r.path for r in members})
+        out.append({
+            "symbol": name, "kind": kind, "key": group,
+            "family": {
+                "group": group, "label": label,
+                "identical": not group.startswith("name:"),
+                "files": files[:_DERIVE_FILES_SHOWN], "file_count": len(files),
+                "size": len(members) + (1 if here is not None else 0),
+            },
+        })
+    return out
+
+
 async def flag_divergence(project_id: int, *, since: datetime | None) -> int:
    """Flag shapes created after ``since`` (the previous refresh) that sit
    where a canon dominates and were not proposed as that canon. With no
@@ -0,0 +1,145 @@
+"""The PostToolUse after-write hook (#2901): code written through Bash — sed,
+heredocs, scripts — gets the same prior-art / ledger checks as a Write/Edit.
+
+Runs the real shell against a temp git repo and a throwaway HTTP sink, like
+the pre-write hook's end-to-end tests. Skips where the hook's tools are
+missing; asserts on content where they are present."""
+from __future__ import annotations
+
+import http.server
+import json
+import os
+import shutil
+import subprocess
+import threading
+import urllib.parse
+from pathlib import Path
+
+import pytest
+
+PLUGIN = Path(__file__).resolve().parents[1] / "plugin"
+HOOK = PLUGIN / "hooks" / "scribe_after_write.sh"
+
+
+def _env(tmp_path, url="http://127.0.0.1:9"):
+    for tool in ("git", "jq", "curl", "bash"):
+        if shutil.which(tool) is None:
+            pytest.skip(f"hook runtime tool {tool!r} not installed")
+    return {"PATH": os.environ["PATH"], "SCRIBE_URL": url, "SCRIBE_TOKEN": "t",
+            "TMPDIR": str(tmp_path), "HOME": str(tmp_path),
+            "GIT_AUTHOR_NAME": "t", "GIT_AUTHOR_EMAIL": "t@x", 
+            "GIT_COMMITTER_NAME": "t", "GIT_COMMITTER_EMAIL": "t@x"}
+
+
+def _repo(tmp_path, env):
+    repo = tmp_path / "repo"
+    repo.mkdir()
+    subprocess.run(["git", "init", "-q"], cwd=repo, check=True, env=env)
+    (repo / "b.py").write_text("def one():\n    return 1\n")
+    (repo / "c.py").write_text("def slug(t):\n    return t.lower()\n")
+    subprocess.run(["git", "add", "."], cwd=repo, check=True, env=env)
+    subprocess.run(["git", "commit", "-q", "-m", "base"], cwd=repo, check=True, env=env)
+    return repo
+
+
+def _run(repo, env, session="s-after-1", tool="Bash"):
+    out = subprocess.run(
+        ["bash", str(HOOK)],
+        input=json.dumps({"session_id": session, "cwd": str(repo), "tool_name": tool,
+                          "tool_input": {"command": "cat > x"}, "tool_response": {}}),
+        capture_output=True, text=True, env=env,
+    )
+    assert out.returncode == 0, out.stderr
+    return out.stdout
+
+
+class _Sink(http.server.BaseHTTPRequestHandler):
+    seen: list[dict] = []
+    reply = b'{"context":"> family named","note_ids":[],"sync_note_ids":[],"derive_keys":["dup:483a"]}'
+
+    def do_GET(self):
+        type(self).seen.append(urllib.parse.parse_qs(urllib.parse.urlparse(self.path).query))
+        self.send_response(200)
+        self.send_header("Content-Type", "application/json")
+        self.end_headers()
+        self.wfile.write(type(self).reply)
+
+    def log_message(self, *a):
+        pass
+
+
+@pytest.fixture
+def sink():
+    _Sink.seen = []
+    server = http.server.HTTPServer(("127.0.0.1", 0), _Sink)
+    threading.Thread(target=server.serve_forever, daemon=True).start()
+    try:
+        yield server
+    finally:
+        server.shutdown()
+
+
+def test_after_write_names_what_bash_just_wrote_then_stays_quiet_until_the_next_change(tmp_path, sink):
+    env = _env(tmp_path, url=f"http://127.0.0.1:{sink.server_port}")
+    repo = _repo(tmp_path, env)
+    # "A Bash call" wrote an untracked stylesheet and appended to a tracked file.
+    (repo / "a.css").write_text(".log-empty {\n  color: red;\n}\n")
+    (repo / "b.py").write_text("def one():\n    return 1\n\ndef slug(t):\n    return t\n")
+    out = _run(repo, env)
+    by_path = {q["path"][0]: q for q in _Sink.seen}
+    assert set(by_path) == {"a.css", "b.py"}           # repo-relative, like the pre hook
+    assert by_path["a.css"]["shapes"] == ["css:log-empty"]
+    assert by_path["b.py"]["shapes"] == ["sym:slug"]
+    # Added lines only for the tracked file — the existing def is not "just written".
+    assert "def slug" in by_path["b.py"]["code"][0] and "def one" not in by_path["b.py"]["code"][0]
+    ctx = json.loads(out)["hookSpecificOutput"]
+    assert ctx["hookEventName"] == "PostToolUse"
+    assert "> family named" in ctx["additionalContext"]
+    # The local by-name arm rides along: `slug` already lives in c.py.
+    assert "`slug` is already defined in 1 other file(s): c.py" in ctx["additionalContext"]
+    # Derive keys landed on the SHARED channel the pre-write hook reads.
+    state = tmp_path / "scribe-priorart" / "s-after-1.derive.ids"
+    assert "dup:483a" in state.read_text().split()
+
+    # Nothing changed → one git status, no request, no output.
+    _Sink.seen = []
+    assert _run(repo, env) == ""
+    assert _Sink.seen == []
+
+    # Another change → only that file, and the dedup channel goes back up.
+    (repo / "a.css").write_text(".log-empty {\n  color: red;\n}\n.other {\n  margin: 0;\n}\n")
+    _run(repo, env)
+    assert [q["path"][0] for q in _Sink.seen] == ["a.css"]
+    assert _Sink.seen[0]["exclude_derive"] == ["dup:483a"]
+    assert set(_Sink.seen[0]["shapes"][0].split(",")) == {"css:log-empty", "css:other"}
+
+
+def test_after_write_is_silent_where_it_has_nothing_to_say(tmp_path):
+    env = _env(tmp_path)
+    repo = _repo(tmp_path, env)
+    # Not a Bash call → nothing (hooks.json matches Bash, the script re-checks).
+    (repo / "a.css").write_text(".x {\n  color: red;\n}\n")
+    assert _run(repo, env, tool="Write") == ""
+    # Not a git repo → nothing.
+    loose = tmp_path / "loose"
+    loose.mkdir()
+    (loose / "a.css").write_text(".x {\n  color: red;\n}\n")
+    assert _run(loose, env, session="s-loose") == ""
+    # A change that defines nothing (prose, a call-site edit) → nothing, even
+    # with the server unreachable (port 9 refuses): no definitions, no arms.
+    (repo / "README.md").write_text("# notes\n")
+    (repo / "b.py").write_text("def one():\n    return one_more()\n")
+    assert _run(repo, env, session="s-quiet") == ""
+
+
+def test_after_write_local_arm_and_record_nudge_work_without_a_server(tmp_path):
+    """The local by-name arm needs no instance (#2280) and the record nudge
+    (#2664) fails open with it — a refused connection stands in for the
+    instance."""
+    env = _env(tmp_path)
+    repo = _repo(tmp_path, env)
+    (repo / "d.py").write_text("def slug(t):\n    return t.lower()\n")
+    out = _run(repo, env, session="s-local")
+    ctx = json.loads(out)["hookSpecificOutput"]["additionalContext"]
+    assert "`slug` is already defined in 1 other file(s): c.py" in ctx
+    assert "create_snippet" in ctx
@@ -597,6 +597,82 @@ async def test_derive_groups_land_on_rows_and_in_the_summary(seeded):
    assert {r.symbol for r in rows} == {"slug"}                   # 2 files < the name floor


+@pytest.mark.integration
+async def test_write_time_derive_names_the_family_or_the_canon_for_a_name(seeded):
+    """#2900: against real rows — a name in a dup family → the family (other
+    files, count); a name whose canonical row lives elsewhere → that canon;
+    a judged row at the path, the canon's own file, or an unknown name →
+    silence."""
+    from scribe.services.shape_ledger import apply_derive_groups, write_time_derive
+
+    owner, pid, sid = seeded["owner"], seeded["pid"], seeded["snippet"]
+    defs = _defs(
+        ("v/A.vue", "css", "log-empty", ".log-empty {", ".log-empty { color: red }"),
+        ("v/B.vue", "css", "log-empty", ".log-empty {", ".log-empty { color: red }"),
+        ("v/C.vue", "css", "log-empty", ".log-empty {", ".log-empty { color: red }"),
+        ("src/factory.py", "sym", "factory", "def factory():", "def factory():\n    return 1"),
+    )
+    await sync_repo_shapes(pid, REPO, defs, seen_marker="m1")
+    await classify_shapes(owner, pid, [
+        {"path": "src/factory.py", "symbol": "factory", "status": "canonical", "snippet_id": sid},
+    ])
+    assert await apply_derive_groups(pid) >= 3
+
+    # A 4th copy about to be written → the family, naming the other files.
+    out = await write_time_derive(pid, "v/D.vue", [("css", "log-empty"), ("css", "unknown")])
+    assert len(out) == 1 and out[0]["symbol"] == "log-empty" and out[0]["kind"] == "css"
+    fam = out[0]["family"]
+    assert fam["identical"] is True and fam["label"] == ".log-empty"
+    assert fam["files"] == ["v/A.vue", "v/B.vue", "v/C.vue"] and fam["file_count"] == 3
+    assert out[0]["key"] == fam["group"] and fam["group"].startswith("dup:")
+    # Editing one existing member still names the OTHER members.
+    out = await write_time_derive(pid, "v/A.vue", [("css", "log-empty")])
+    assert out[0]["family"]["files"] == ["v/B.vue", "v/C.vue"] and out[0]["family"]["size"] == 3
+    # The canon's name elsewhere → the canon; in the canon's own file → silence.
+    out = await write_time_derive(pid, "src/other.py", [("sym", "factory")])
+    assert out == [{"symbol": "factory", "kind": "sym", "key": f"canon:{sid}",
+                    "canon": {"snippet_id": sid, "path": "src/factory.py", "label": "factory"}}]
+    assert await write_time_derive(pid, "src/factory.py", [("sym", "factory")]) == []
+    # A judged row at the path is not re-litigated.
+    await classify_shapes(owner, pid, [
+        {"path": "v/B.vue", "symbol": "log-empty", "status": "exempt", "reason": "print sheet"},
+    ])
+    assert await write_time_derive(pid, "v/B.vue", [("css", "log-empty")]) == []
+
+
+@pytest.mark.integration
+async def test_derive_new_names_the_copy_that_joined_a_family_since_the_stamp(seeded):
+    """#2899: the first sync seeds one `slug`; a later sync adds an identical
+    copy. Against the stamp between them, derive_new counts ONLY the
+    newcomer — the drift since the last refresh, not the whole family."""
+    from datetime import datetime, timezone
+
+    from scribe.services.shape_ledger import (
+        apply_derive_groups, derive_new_summary, live_rows,
+    )
+
+    owner, pid = seeded["owner"], seeded["pid"]
+    first = _defs(
+        ("a/one.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+    )
+    await sync_repo_shapes(pid, REPO, first, seen_marker="m1")
+    stamp = datetime.now(timezone.utc)
+    second = _defs(
+        ("a/one.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+        ("a/two.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+    )
+    await sync_repo_shapes(pid, REPO, second, seen_marker="m2")
+    assert await apply_derive_groups(pid) == 2
+
+    rows = await live_rows(pid)
+    out = derive_new_summary(rows, since=stamp)
+    assert out["count"] == 1
+    assert out["examples"][0]["path"] == "a/two.py"
+    assert out["examples"][0]["label"] == "slug"
+    assert out["examples"][0]["group"].startswith("dup:")
+    assert derive_new_summary(rows, since=None)["count"] == 0
+
+
 # --- #2793: the divergence readout against real rows -------------------------


@@ -276,6 +276,8 @@ async def test_coverage_measures_the_tree_exactly_and_caches(seeded):
    assert coverage["largest_gaps"] == [
        {"dir": "src", "unclassified": 2, "total": 3}
    ]
+    # #2899: a first computation has no previous stamp — nothing is "new".
+    assert coverage["derive_new"] == {"count": 0, "examples": []}

    # The walk fed the LEDGER (#2788): every extracted shape has a row, the
    # snippet reference locations are mechanically stamped canonical WITH
@@ -512,6 +514,41 @@ def test_coverage_line_names_the_proposers_standing():
    assert "top canon #2844 ×78" in line and "top copy closed-msg (identical body) ×3 files" in line


+def test_coverage_line_shows_standing_work_even_with_nothing_unclassified():
+    """#2899: since the scoped bucket a ledger can be fully accounted and
+    still carry derive groups / proposals / divergence — the line names
+    them as `standing:` instead of hiding them behind the todo count, and
+    names the drift since the previous refresh first-copy-first."""
+    from scribe.services.coverage import coverage_line
+
+    base = {
+        "total": 4693, "accounted": 4693, "unclassified": 0,
+        "counts": {"canonical": 37, "instance": 977, "variant": 73, "exempt": 1797, "scoped": 1809},
+        "computed_at": "2026-08-22T00:00:00+00:00", "largest_gaps": [],
+    }
+    quiet = coverage_line(base)
+    assert "unclassified" not in quiet and "standing" not in quiet
+    line = coverage_line({
+        **base,
+        "derive_groups": [{"group": "dup:abc", "label": "log-empty (identical body)", "files": 4}],
+        "derive_new": {"count": 2, "examples": [
+            {"label": ".error-msg", "path": "frontend/src/components/InceptionCard.vue", "group": "dup:9f0"},
+            {"label": ".error-msg", "path": "frontend/src/components/Other.vue", "group": "dup:9f0"},
+        ]},
+        "divergent": 1,
+    })
+    assert "; standing: 1 derive group, +2 new copies since last refresh: .error-msg in " \
+           "frontend/src/components/InceptionCard.vue, 1 DIVERGENT, top copy log-empty (identical body) ×4 files" in line
+    assert "unclassified" not in line
+    # One copy reads singular; with a todo the block keeps its old place.
+    one = coverage_line({**base, "derive_new": {"count": 1, "examples": []}})
+    assert one.endswith("; standing: +1 new copy since last refresh")
+    todo = coverage_line({**base, "unclassified": 3, "accounted": 4690, "proposed": 2,
+                          "derive_new": {"count": 1, "examples": [{"label": "x", "path": "a.py"}]},
+                          "largest_gaps": [{"dir": "src", "unclassified": 3, "total": 9}]})
+    assert "; 3 unclassified (2 proposed, +1 new copy since last refresh: x in a.py), largest: src" in todo
+
+
 def test_coverage_line_names_divergence_and_recheck():
    from scribe.services.coverage import coverage_line

@@ -317,6 +317,38 @@ def test_derive_groups_copy_before_name_with_floors():
    assert ("i.py", "sym", "one") not in g


+def test_derive_new_summary_counts_copies_first_seen_since_the_previous_refresh():
+    """#2899: the arrival-moment drift signal — derive-grouped rows created
+    after the previous refresh's stamp, newest first, judged rows and a
+    first seed (since=None) never count."""
+    from datetime import datetime, timedelta, timezone
+
+    from scribe.models.code_shape import CodeShape
+    from scribe.services.shape_ledger import derive_new_summary
+
+    t0 = datetime(2026, 8, 22, 12, 0, tzinfo=timezone.utc)
+
+    def row(path, symbol, at, kind="css", status="scoped", group="dup:abc", basis="derive"):
+        r = CodeShape(project_id=2, repo_key="r", path=path, symbol=symbol, kind=kind,
+                      status=status, proposal_basis=basis, proposal_group=group)
+        r.created_at = at
+        return r
+    rows = [
+        row("v/Old.vue", "error-msg", t0 - timedelta(days=3)),              # before the stamp
+        row("v/InceptionCard.vue", "error-msg", t0 + timedelta(hours=1)),   # new copy
+        row("v/Other.vue", "error-msg", t0 + timedelta(hours=2)),           # newer copy
+        row("v/J.vue", "error-msg", t0 + timedelta(hours=3), status="exempt"),   # judged: never
+        row("s/a.py", "load", t0 + timedelta(hours=1), kind="sym", group=None, basis=None),  # no family
+    ]
+    out = derive_new_summary(rows, since=t0)
+    assert out["count"] == 2
+    assert [e["path"] for e in out["examples"]] == ["v/Other.vue", "v/InceptionCard.vue"]
+    assert out["examples"][0] == {"label": ".error-msg", "path": "v/Other.vue", "group": "dup:abc"}
+    assert derive_new_summary(rows, since=None) == {"count": 0, "examples": []}
+    assert derive_new_summary(rows, since=t0, top=1)["examples"] == [
+        {"label": ".error-msg", "path": "v/Other.vue", "group": "dup:abc"}]
+
+
 def test_proposal_summary_ranks_body_identical_groups_first_and_sees_scoped_rows():
    """#2872: dup groups (the real copies) outrank name groups (usually
    convention), wider spread first; #2869: scoped rows are in the readout."""
@@ -853,14 +853,18 @@ def test_hook_exits_silently_when_unconfigured():


 def test_hook_skips_prose_and_data_files():
-    """No round-trip for a markdown edit — the server would return nothing anyway."""
-    src = HOOK.read_text()
-    skip = re.search(r"case \"\$file_path\" in\n(.*?)esac", src, re.S)
-    assert skip, "expected an extension skip list"
+    """No round-trip for a markdown edit — the server would return nothing
+    anyway. The list lives in the shared library (#2901) and the hook asks it."""
+    lib = (PLUGIN / "hooks" / "scribe_defs.sh").read_text()
+    skip = re.search(r"scribe_skip_path\(\) \{\n  case \"\$1\" in\n(.*?)esac", lib, re.S)
+    assert skip, "expected an extension skip list in scribe_defs.sh"
    for ext in ("*.md", "*.json", "*.lock", "*.png"):
        assert ext in skip.group(1)
    # Config formats are deliberately NOT skipped — a workflow file is reusable.
    assert "*.yml" not in skip.group(1)
+    src = HOOK.read_text()
+    assert 'scribe_skip_path "$file_path" && exit 0' in src
+    assert '/scribe_defs.sh"' in src                   # sourced, not copied


 def test_plugin_version_bumped_with_the_hook():
@@ -1150,7 +1154,9 @@ def test_hook_names_the_shapes_being_written():
    that changes a body, not a signature — the definition enclosing the edit,
    found by walking the target file upward from the edited lines."""
    src = HOOK.read_text()
-    assert "scribe_defs()" in src                      # one extractor, two consumers
+    lib = (PLUGIN / "hooks" / "scribe_defs.sh").read_text()
+    assert "scribe_defs()" in lib                      # one extractor, shared (#2901)
+    assert "scribe_defs()" not in src                  # ...not a second copy here
    assert ".tool_input.old_string" in src             # the Edit's anchor
    assert "| tac | scribe_defs | head -1" in src      # nearest definition above
    # The ledger feed sends NAMES, never bodies, and stays on the one GET.
@@ -1243,6 +1249,116 @@ def test_hook_sends_the_enclosing_definition_for_a_body_edit(tmp_path):
    assert seen["shapes"] == ["sym:onTrash"]


+@pytest.mark.asyncio
+async def test_the_write_time_derive_check_names_a_family_or_a_canon_in_band():
+    """#2900: the ledger's own word on the names being written — a duplicate
+    family with no canon, or a canon recorded elsewhere — rendered at the
+    write even when nothing else does; keyed so the session's exclude
+    channel silences a family already named."""
+    from scribe.services import plugin_context as pc
+    found = [
+        {"symbol": "log-empty", "kind": "css", "key": "dup:483a",
+         "family": {"group": "dup:483a", "label": ".log-empty", "identical": True,
+                    "files": ["a/TaskLogSection.vue", "a/WorkspaceTaskPanel.vue"],
+                    "file_count": 5, "size": 6}},
+        {"symbol": "btn-primary", "kind": "css", "key": "canon:2855",
+         "canon": {"snippet_id": 2855, "path": "frontend/src/assets/components.css",
+                   "label": ".btn-primary"}},
+        {"symbol": "load", "kind": "sym", "key": "name:sym:load",
+         "family": {"group": "name:sym:load", "label": "load", "identical": False,
+                    "files": ["a/X.vue", "a/Y.vue", "a/Z.vue"], "file_count": 3, "size": 4}},
+    ]
+    check = AsyncMock(return_value=found)
+    patches = dict(
+        get_writepath_config=AsyncMock(return_value=_cfg()),
+        semantic_search_notes=AsyncMock(return_value=[]),
+        record_retrieval=MagicMock(), owner_names_for=AsyncMock(return_value={}),
+    )
+    with patch.multiple(pc, **patches), \
+         patch.object(pc.snippets_svc, "list_snippets", AsyncMock(return_value=([], 0))), \
+         patch.object(pc.shape_ledger_svc, "recent_pulls", AsyncMock(return_value={})), \
+         patch.object(pc.shape_ledger_svc, "write_time_divergence", AsyncMock(return_value=[])), \
+         patch.object(pc.shape_ledger_svc, "write_time_derive", check):
+        out = await pc.build_write_path_hint(
+            1, "frontend/src/components/New.vue", code=REAL_CODE, project_id=24,
+            stamp_shapes=[("css", "log-empty"), ("css", "btn-primary"), ("sym", "load")],
+            exclude_derive=["name:sym:load"],
+        )
+    check.assert_awaited_once_with(24, "frontend/src/components/New.vue",
+                                   [("css", "log-empty"), ("css", "btn-primary"), ("sym", "load")])
+    # The excluded family is gone; the other two render and are keyed.
+    assert [d["key"] for d in out["derive"]] == ["dup:483a", "canon:2855"]
+    assert out["derive_keys"] == ["dup:483a", "canon:2855"]
+    ctx = out["context"]
+    assert "Shape ledger at `frontend/src/components/New.vue`" in ctx
+    assert "`.log-empty` is a duplicate family with no canon — identical body in 5 other file(s): " \
+           "`a/TaskLogSection.vue`, `a/WorkspaceTaskPanel.vue` +3 more; derive it now" in ctx
+    assert "`.btn-primary` is canon — snippet #2855 at `frontend/src/assets/components.css`" in ctx
+    assert "convention-plumbing" in ctx
+    assert "`load`" not in ctx
+    # No project → no check; a failing check never sinks the hint.
+    check.reset_mock()
+    with patch.multiple(pc, **patches), \
+         patch.object(pc.snippets_svc, "list_snippets", AsyncMock(return_value=([], 0))), \
+         patch.object(pc.shape_ledger_svc, "recent_pulls", AsyncMock(return_value={})), \
+         patch.object(pc.shape_ledger_svc, "write_time_divergence", AsyncMock(return_value=[])), \
+         patch.object(pc.shape_ledger_svc, "write_time_derive", check):
+        out = await pc.build_write_path_hint(1, "x.py", code=REAL_CODE, stamp_shapes=[("sym", "f")])
+    check.assert_not_awaited()
+    assert out["derive"] == [] and out["derive_keys"] == []
+    boom = AsyncMock(side_effect=RuntimeError("ledger down"))
+    with patch.multiple(pc, **patches), \
+         patch.object(pc.snippets_svc, "list_snippets", AsyncMock(return_value=([], 0))), \
+         patch.object(pc.shape_ledger_svc, "recent_pulls", AsyncMock(return_value={})), \
+         patch.object(pc.shape_ledger_svc, "write_time_divergence", AsyncMock(return_value=[])), \
+         patch.object(pc.shape_ledger_svc, "write_time_derive", boom):
+        out = await pc.build_write_path_hint(1, "x.py", code=REAL_CODE, project_id=24,
+                                             stamp_shapes=[("sym", "f")])
+    assert out["context"] == "" and out["derive"] == []
+
+
+def test_the_hook_keeps_a_derive_channel_and_sends_it_back(tmp_path):
+    """#2900: derive keys the server returns land in the session's own
+    `.derive.ids` file and go back as `exclude_derive` on the next write —
+    a family is named once per session, not at every edit."""
+    import http.server
+    import threading
+    import urllib.parse
+
+    seen: list[dict] = []
+
+    class _Sink(http.server.BaseHTTPRequestHandler):
+        def do_GET(self):
+            seen.append(urllib.parse.parse_qs(urllib.parse.urlparse(self.path).query))
+            self.send_response(200)
+            self.send_header("Content-Type", "application/json")
+            self.end_headers()
+            self.wfile.write(b'{"context":"> family","note_ids":[],"sync_note_ids":[],'
+                             b'"derive_keys":["dup:483a","canon:2855"]}')
+
+        def log_message(self, *a):
+            pass
+
+    server = http.server.HTTPServer(("127.0.0.1", 0), _Sink)
+    threading.Thread(target=server.serve_forever, daemon=True).start()
+    try:
+        env = dict(_hook_runtime_env(), SCRIBE_URL=f"http://127.0.0.1:{server.server_port}",
+                   TMPDIR=str(tmp_path))
+        payload = {"session_id": "s-derive-1", "cwd": str(tmp_path), "tool_name": "Write",
+                   "tool_input": {"file_path": str(tmp_path / "a.css"),
+                                  "content": ".log-empty {\n  color: red;\n}\n"}}
+        for _ in range(2):
+            out = subprocess.run(["bash", str(HOOK)], input=json.dumps(payload),
+                                 capture_output=True, text=True, env=env)
+            assert out.returncode == 0, out.stderr
+    finally:
+        server.shutdown()
+    assert "exclude_derive" not in seen[0]
+    assert seen[1]["exclude_derive"] == ["dup:483a,canon:2855"]
+    state = tmp_path / "scribe-priorart" / "s-derive-1.derive.ids"
+    assert state.read_text().split() == ["dup:483a", "canon:2855", "dup:483a", "canon:2855"]
+
+
@pytest.mark.asyncio
 async def test_the_write_time_divergence_check_is_named_in_band():
    """#2793: the hook named a shape at a path whose directory a canon